Objectives
Discuss soil components, texture and chemistry
Consider relationships between soil, water, plants and air
Examine steps to prevent soil compaction and salt accumulation
Identify common plant nutrient deficiencies in our region
Calculate fertilizer requirements
Review proper techniques in soil analysis collection
• Supports the roots and anchors the above ground plant material
• Provides the essential elements for uptake by trees and plants
• Holds and supplies water and essential elements to the plants
• Releases water vapor into the air, potentially creating a cooler microclimate
Knowing the characteristics of the soil on a particular job site can be the difference between success and failure.
Soil isn’t “Just Dirt”! It is the ecosystem that supports our landscape plants. What we do to it matters.
Function of Soil in the Landscape and Why We Care:
Arizona Desert Soils
Mineral
Alkaline
Arid
Probably some caliche
May be rocky and shallow, particularly in foothills
May be saline
May be heavy
Desert soils have low organic matter because there is not enough precipitation to support lush wild plant growth
Urban Soil Challenges
In general, our desert, urban soils have low organic matter and less pore space
Soil quality directly impacts plant life
Establishment
Growth
Health
Longevity
Organic Matter • Group of carbon containing
compounds
• Originated from living material and have been deposited on or within earths structural components
• Contains minerals and trace elements
Benefits of Organic Matter
• Helps strengthen soil aggregates, thus improving soil structure
• Improve aeration and water infiltration
• Increases water-holding capacity
• Provides significant amounts of cation exchange capacity
• What do we do with organic matter in the landscape? Blow it, bag it and cart it away.
• Mulching grass clippings and leaving some leaf litter as a natural mulch can increase the organic matter content of the soil over time.
Soil Texture Refers to the size of particles that make up the
soil: sand, silt and clay
‘light’ soil
‘heavy’ soils
Heavy, Light or Just Right? Clay • “Heavy”
• Slow infiltration
• High water-holding capacity
• High nutrient-holding capacity
Sand • “Light”
• Fast infiltration
• Low water-holding capacity
• Low nutrient-holding capacity
Physical Properties
Soil
Texture
Triangle
68% sand
18% silt
14% clay
International Society of Arboriculture, Bugwood.org
Can you alter soil texture?
• “You get what you get and you don’t throw a fit!”
• Not practical to try to alter on a large scale
• Not financially feasible on a large scale
• Better to focus on selecting plants that are more
tolerant of current site conditions
Salinity
Sodium(Na), Calcium (Ca), Potassium (K) and salts accumulate in soils
Peeling of the soil surface is a sign of poorly
drained, salty soil and remediation is required for
plants to grow
Salts contained in irrigation water will accumulate unless adequate leaching is provided.
Excess water (more than plants require) must be added to flush salts below the root zone. This excess irrigation is
called the “leaching requirement”.
How does soil become saline?
Shallow watering
Fertilizers
Irrigation water quality
Application of other salty substances to soil
Frequent, shallow irrigation is the leading cause of
salt build up. Watering more deeply and less
frequently helps flush salts out of the root zone of
plants.
Cation Exchange Capacity (CEC)
The total number of cations a soil can hold--or its total negative charge--is the soil's cation exchange capacity. The higher the CEC, the higher the negative charge and the more cations that can be held.
Cations held on the clay and organic matter particles in soils can be replaced by other cations; thus, they are exchangeable. For instance, potassium can be replaced by cations such as calcium or hydrogen, and vice versa.
Cation Exchange Capacity
Cations:
NH4+, K+,
Fe++, Ca++
Anions:
NO3-, SO42-
Humus and clay carry a negative charge, and
so attract positively charged cations
Cation Exchange Video
• https://www.youtube.com/watch?v=HmEyymGXOfI&feature=youtu.be
Sodium Adsorption Ratio (SAR)
The ratio of ‘bad’ to ‘good’ flocculators gives an indication of the relative status of these cations:
+ +
+ + + +
+
Ca2+ and Mg2+ ++
++ ++
++ ++ ++
++
Mathematically, this is expressed as the ‘sodium adsorption ratio’ or SAR:
where concentrations are expressed in mmoles/L
SAR =
[Na+]
[Ca2+] + [Mg2+] 2
Exchangeable Sodium Percentage (ESP)
An alternative to SAR is ESP (Exchangeable Sodium Percentage)
SAR and ESP are approximately equal numerically
Mathematically, this is expressed as the percentage of the CEC (cation
exchange capacity) that is filled with sodium in units of charge per mass
(cmolc/kg)
ESP =
Na+
Cation Exchange Capacity
+ Ca2+ and Mg2+ ++
- - - - - - - - -
+ + +
+
++
++
++
++ ++
Test soil to determine sodium level
Soil sodium tests:
SAR - sodium adsorption ratio
ESP - exchangeable sodium percentage
If SAR or ESP are ≥ 10 the soil is likely to disperse.
You should consider treating the soil.
Lower ESP and SAR numbers are always good
Managing Salt
• Apply extra water to prevent excessive salt buildup
• The amount of extra water needed is called the leaching requirement (LR)
• LR is higher when using salty irrigation water
• LR is higher when growing salt-sensitive plants
• You can save water and prevent salt buildup by using adapted plant species
Salty Soil – Saline or Sodic? Why does it matter? The treatment is different!
• Saline
• Non-sodic soil containing sufficient soluble salt to adversely affect the growth of most crop plants with a lower limit of electrical conductivity of the saturated extract (ECe) being 4 deciSiemens / meter (dS/m), which is equivalent to a value of 4 mmhos/cm
• Sodic
• Non-saline soil containing sufficient exchangeable sodium (Na) to adversely affect crop production and soil structure under most conditions of soil and plant type. The sodium adsorption ratio of the saturation extract (SARe) is at least 13
Salty Soil Treatments
• Sodic soils
• Gypsum applications (replaces Na with Ca)
• Leaching program
• Saline soils
• Leaching program (best way)
• Elemental sulfur applications (soil incorporation is best)
• Sodic-saline soils
• Gypsum applications
• Leaching program
Caliche
• Layer of soil where soil particles have been cemented
together by lime (calcium carbonate, CaCO3)
• Common in arid areas due to low precipitation
• Light in color
• Thickness of layers vary, few inches to several feet thick
• May be more than one layer of caliche in the soil profile
Caliche
• Reduces water movement through soil profile
• Restricts root growth to upper levels of soil (may reduce
growth)
• Leads to salt accumulation and reduced aeration in soil
• High pH can cause nutrient deficiencies in plants,
especially iron
Caliche Management
• Keep roots out of the caliche zone
• Physically remove caliche layers if possible to
allow for water drainage out of root zone
• Check drainage on property prior to planting
by performing a percolation test
• Dig plant hole, fill with water and confirm
drainage is at rate of 4” per 4 hours
• Utilize chimney drainage holes to provide
drainage
Soil Amendments
Used to modify soil chemistry in our region Gypsum (Calcium sulfate)
temporarily removes Na from soil, helps break apart hardened soils
Soil sulfur
may eventually reduce pH after repeated applications
Organic matter
Microbial degradation and production of organic acids
Large amounts are required
Fertilizers
Ammonium products (especially ammonium sulfate)
Observe the soil:
Soil cracks when dry
Soil won’t absorb water
Rainwater soaks in more slowly than irrigation water
How do you know if you need to apply gypsum?
Soil Amendments
Elemental Sulfur
• Slow reaction- may take many months to change pH
• Dependent on microbial action (Thiobacillus)
• Soil incorporation is necessary
• Sulfur neutralizes the free calcium carbonate
• Not practical to change soil pH over large areas, but may be appropriate for directed applications to specific plants
• Monitor results with soil sample to confirm desired pH is achieved
Sulfur is oxidized by bacteria to form sulfuric acid
S + O2 + H2O = H2SO4
(elemental S + oxygen + water + soil microorganisms + time =
sulfuric acid)
Capillary Action
Cohesion – “like sticking to like”
Water molecules stick together
Adhesion – “sticking to unlike”
Water molecules stick to certain surfaces
Capillary action – drawing of water in a narrow tube
Soil Compaction
Compaction reduces pore space:
Restricts H2O and O2= Poor root development
Increased density of soil by packing the soil particles closer
together causing a reduction in the volume of air.
1-2-3 Rule of Irrigation
Watering depth
1 ft - Flowers, vegetables and other small annuals
2 ft – Shrubs
3 ft – Trees
AMWUA.org
Essential Plant Elements
• Needed in larger amounts
• Primary macronutrients
• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)
• Secondary macronutrients
• Calcium
• Sulfur
• Magnesium
• Needed in smaller amounts
• Iron
• Boron
• Manganese
• Zinc
• Copper
• Chlorine
• Molybdenum
• Nickle* * recently added
• Other essential plant elements include Hydrogen, Carbon & Oxygen
Macronutrients
Micronutrients
Soil Testing
• Find a local, reliable lab – see AZ Cooperative
Extension Publication AZ1111 in the resources
• Collect a representative sample – ask your lab for
specifics or see AZ Coop Ext Publication AZ1412
• Make decisions based on the results - pay extra for
the recommendations – worth it unless you are very
experienced
Nitrogen (N)
• Originates from decomposing organic material,
from rainfall and from nitrogen-fixing bacteria
• Generally, in short supply in western (desert)
soils
• Required in large amounts by plants
• Readily lost through leaching & microbe activity
To get quick ‘greening’, use a
fertilizer with nitrogen in the
ammonic form
Examples: Ammonium Sulfate (21-0-0)
Ammonium Nitrate (33-0-0)
Nitrogen Deficiency
• Nitrogen (N)
• Yellowing of older leaves, bottom of plant
• Rest of the plant is often light green
• Stunted growth
• Foliage may drop early in fall
• Mobile in plants so overwatering can cause deficiency
• Treatment
• Ammonium, Urea, Nitrate, manures, blood meal
Phosphorus Deficiency • Phosphorus (P)
• Leaf tips look burnt
• Older leaves turning a dark green or reddish purple
• Stunting
• Loss of lower leaves
• Poor root growth
• Mobile in plants
• Treatment
• Phosphate products
• Bone meal
• Greensand
Iron Deficiency • Iron (Fe)
• Interveinal chlorosis (yellowing leaf with green veins)
• Found on newer growth
• Leaves may be small
• Immobile in plants
• Treatment
• Iron chelates
• Ferrous sulfate
Zinc Deficiency
• Zinc (Zn)
• New leaves interveinal chlorosis, thicker green pattern around veins
• Necrotic spots on margins or tips
• Dwarfed new leaves, cupped upward or distorted
Deficiency on citrus, normal leaf on right
Other Micronutrient Deficiencies
Zinc (Z) Deficiency
Manganese (Mn) Deficiency
Magnesium (Mg) Deficiency
• Micronutrient deficiencies may be
caused by multiple minerals lacking
• Application of micronutrient packages
will help broaden the spectrum
• Foliar testing to confirm mineral
deficiency
Understanding Soil pH
https://www.youtube.com/watch?v=7Z15h189LCc
Treating Plants in Alkaline Soils
• Metal nutrients are insoluble in alkaline soils (iron, manganese, zinc)
• Apply nutrients directly to plant foliage
• use sulfate salts
• iron sulfate
• copper sulfate
• zinc sulfate
• Use chelated forms
• more soluble than un-chelated forms
• stay in solution longer
• more available to plants
• EDTA
• DTPA
• others
Other Factors Affecting Uptake
Raises Fertility Lowers Fertility
High clay content High sand content
High humus content Loss of organic matter
Good structure Compaction
Warm soil Cold soil
Deep soil Shallow soil
Moist soil Dry or wet soil
Good drainage Excess irrigation or drainage
Fertilization Erosion
Desirable microbes Root damaging pests
Near neutral pH pH too acid or alkaline
Fertilizers
Add nutrients to the soil
Organic and inorganic forms
Usually salts
Can burn plants
Must be watered in
Fertilizer analysis N-P2O5-K2O (nitrogen-phosphate-potash)
• Complete fertilizer • 21-7-14 (contains N-P-K)
• Incomplete fertilizer • 21-0-0 (contains only N)
• Slow release fertilizers • Coated to promote slow
release of minerals
Organic vs. Chemical Fertilizers
Organic
• Often recycle waste materials
• May be resource intensive
• Can be bulky, heavy
• Micronutrients
• May contain pathogens, weeds
• Salt
• Requires more fertilizer to get the same amount of N as chemical fertilizer
• Generally slow-release
• Can improve soil structure as they break down
Chemical (Inorganic) • Can be energy intensive to
make
• Lighter weight
• Less material required
• Minerals in formulations readily available for plants
• Must be purchased
• Salt
• May provide more predictable results
• More risk of over fertilization
Organic vs. Chemical Fertilizers Organic
• Manure
• Compost
• Fish emulsion
• Guano
• Milorganite
• Bone meal, blood meal
• Cottonseed meal
Chemical/ Inorganic
• Ammonium nitrate
• Ammonium sulfate
• Urea
• Superphosphate
• Potassium nitrate
• Calcium nitrate
Determining the amount of a fertilizer for a given area
1. Take the measurements (in feet) of the area in question
2. Multiply the length by the width; this gives you the area in square feet (sq ft.)
3. Read the label. Determine how much product is required per 1000 sq. ft. Measure the amount fertilizer needed
4. Calibrate your spreader, load and distribute
Example #1 A lawn is 100 by 50 ft. How much fertilizer is necessary if the
label states that you need 1 lb. of the product per 1000 square feet?
Determine the area. 100 ft. X 50 ft. = 5000 sq. ft.
Since you need 1 lb. of fertilizer/ 1000 sq. ft. Divide
5000 sq.ft. by 1000
This tells you how many 1000 sq. ft. units there are in the lawn. This is 5.
5 x 1 lb/1000 = 5 lbs per 5000 sq.ft. Answer is 5 lbs.
Example # 2 How many lbs. of 16-20-0, applied to a 50’ by 20’ lawn, requiring 1 lb. of nitrogen per 1000 sq. ft.?
Step 1: Determine the area 50’ X 20’ = 1000 sq. ft.
Step 2: Calculate how many pounds of 16-20-0 it takes to get one pound of nitrogen (N)
Divide 100 by 16 (101.6 or 1 0.16 same results) 100 16 = 6.25 lbs. of 16-20-0
50 feet
20 feet
Example 3:
How many pounds of 16-20-0 should be applied to a lawn measuring 50’ by 40’ that requires 2 lbs of phosphorus per 1000 sq. ft.?
Step 1: Determine the area.
50 ft. X 40 ft. = 2000 sq. ft.
Step 2: Determine the number of lbs. of 16-20-0 to get 1 lb of Phosphorous. 100 divided by 20 = 5 lbs.
(5 lbs of 16-20-0 has 1 lb of Phosphorus)
50 feet
40 feet
Step 3: Calculate the number of lbs of 16-20-0 that supplies the rate of 2 lbs. of phosphorus per 1000 sq. ft.
Remember that 5 lbs of 16-2-0 has 1 lb of phosphate
2 x 5 lbs = 10 lbs of ammonium phosphate
Your rate of 16-20-0 is:
10 lbs/1000 sq ft to apply 2 lbs of P per 1000 sq ft
Spreader Calibration
https://www.youtube.com/watch?v=BT4kzNq7750
You can apply these principals to calibrating a drop spreader and handheld belly-grinder.
Resources • Laboratories Conducting Soil, Plant, Feed, or Water Testing
• https://extension.arizona.edu/pubs/laboratories-conducting-soil-plant-feed-or-water-testing
• Fertilizing Home Gardens in Arizona
• http://extension.arizona.edu/pubs/fertilizing-home-gardens-arizona
• Soil Sampling and Analysis
• http://extension.arizona.edu/pubs/soil-sampling-and-analysis
• Using Gypsum and Other Calcium Amendments in Southwestern Soils
• https://extension.arizona.edu/pubs/using-gypsum-other-calcium-amendments-southwestern-soils
• Diagnosing Nutrient Deficiencies Quick-Reference
• https://extension.arizona.edu/pubs/diagnosing-nutrient-deficiencies-quick-reference
• Nitrogen in Soil and the Environment
• https://extension.arizona.edu/pubs/nitrogen-soil-and-environment
• Recognizing and Treating Iron Deficiency in the Home Yard
• https://extension.arizona.edu/pubs/recognizing-treating-iron-deficiency-home-yard
• University of Arizona publication search
• https://extension.arizona.edu/pubs
Soil Testing Laboratories
Local
IAS Laboratories 602-273-7248
2515 E. University Dr. Phoenix, AZ
Motzz Laboratory, Inc. 602-454-2376
3540 E. Corona Ave. Phoenix, AZ
National
AgSource/ Harris Labs 402-476-0300
harrislabs.agsource.com
Thank you to those who contributed to this program:
Rebecca Senior University of Arizona Cooperative Extension Maricopa County
602-827-8276 Office 602-509-6719 Cell [email protected]
Kasey Billingsley
Harmony Horticultural Consulting, LLC